Connecting conduits for fluids

ABSTRACT

The disclosed method &amp; apparatus are for forming a fluid connection or tap through the wall of a pipeline, particularly intended for “hot tapping” of subsea pipelines. The method comprises fitting a connecting piece having a mounting surface which extends around the tap location and at least partially over the tap location and a connecting wall ( 2 h) which surrounds the tap location to provide an opening adapted for subsequent connection of a conduit to complete a fluid connection. The connecting piece is bonded to the pipeline by friction stitch welding performed inside said opening. The material at the tap location is removed (AC indicates after cutting) to define an aperture and provide said fluid connection surrounded closely by the weld between the connecting piece and the wall.

This invention relates to a method of welding a connecting piece to apipeline or other vessel, to provide a fluid connection. The inventionis particularly suitable for “hot-tapping”, in which a branch connectionis made onto an existing installation without interrupting the operationthereof. The invention may be applied generally in the constructionand/or maintenance of fluid-handling installations, however, bothonshore and offshore.

At present, the attachment of such fittings is effected either by theuse of a fusion welding process or a mechanical clamp fitted with anon-metallic seal for pressure and fluid containment. A typicalapplication of hot tapping is installing a branch connection to apipeline and cutting into a pressurised pipeline without interruptingthe flow of the fluids in the pipeline. It may also be used to fit avalve or other equipment to a vessel or tank.

Mechanical hot tapping clamps are designed to provide structuralintegrity and are of heavy construction and high cost. The sealingelements are manufactured in non-metallic materials and are subject todegradation when exposed to some fluids.

Fusion welding is typically done using arc welding techniques. Aconnecting wall (pipe stub), and a sleeve or saddle piece are generallywelded around the tap location, and the finally a section of the pipewall is removed from inside the stub. Standard forms of hot tappingjoints with sleeves and/or saddles and different welding sequences arediscussed in ASME Code for Pressure Piping B31. In welding a hot tapconnection, it is necessary to pre-heat the weld area to avoiddetrimental metallurgical effects and hydrogen cracking. Due to the highcooling effect of the fluids inside the pipeline, it is necessary toprovide very intense heating methods such as induction of flame heating.

Maintaining adequate pre-heat temperature when welding hot-taps onpipes, tubulars or vessels containing fluids is extremely difficult. Forexample, flame heating torches are applied for several minutes in orderto raise the temperature of the joint and welding can only be done for abrief period before the torches must be applied again. This is timeconsuming and accurate monitoring of the pre-heat-temperature isdifficult Furthermore, there is a safety problem with using torchesclose to welders and serious accidents have occurred.

One successful alternative is to use induction heating to maintain therequired temperature, as suggested in GB 2 213 276 and GB 2 214 118.However, the electrical power requirements are high (typically 300 kW)and this may be difficult to provide at remote locations. Furthermore,the induction heating and power generating equipment is costly, heavyand cumbersome.

For underwater attachments and hot tapping it is only possible toachieve acceptable weld integrity by working in a dry hyperbaricenvironment, as the high pressures experienced otherwise tend to drivegasses into the structure formed and weaken it.

WO-A-93/04813 (U.S. Pat. No. 5,469,617) proposes an alternative weldingmethod known as Friction Stitch Welding. In this method of welding, ahole is bored through one workpiece and into the workpiece to which itis to be joined. A plug is then inserted into the bored hole and rotatedunder pressure. The frictional heat generated during this melts the plugwhich when allowed to cool forms a weld. A continuous welded joint maybe built up from a number of these welds.

For further data on this general welding technique attention is drawn tothe following articles:

-   -   Engineering Applications of Friction Stitch Welding—Gibson, D et        al and Considerations On Robotic Friction Stitch Welding For The        Repair of Marine Structures—Meyer A et al        both at Proceedings of ETCE/OMAE 2000 Joint Conference: Energy        for the Millennium Feb. 14-17 2000 New Orleans, USA. The first        article mentioned above makes the suggestion to employ friction        stitch welding for hot tapping applications. However, the need        to apply forces of many kN at high rotational speeds makes it        difficult to apply the known devices for welding the lengthy and        convoluted outlines of a hot tapping saddle.

The present invention is concerned with providing an improved method offorming a fluid connection onto a pipeline or other vessel. Inparticular, a hot tapping method is sought, for underwater application,in which one or more of the above mentioned problems are alleviated.

The invention in a first aspect provides a method of forming a fluidconnection (hereinafter referred to as a tap) through a first wall at adesired tap location, the method comprising:

-   -   fitting against the first wall a connecting piece which        comprises (i) a mounting surface formed so as to fit against the        first wall, the material of said mounting surface extending        around the tap location and (ii) a connecting wall surrounding        the tap location providing an opening adapted for subsequent        connection of a conduit to complete said fluid connection, the        material of said mounting surface further extending at least        partially within said opening;    -   bonding the material of the connecting piece to that of the        first wall by means of a welding operation performed through        said opening, the resulting weld surrounding the tap location        and being surrounded in turn by the connecting wall; and    -   removing the material of the first wall at the tap location        thereby to define an aperture and provide said fluid connection        surrounded by the weld between the connecting piece and the        wall.

By performing the welding operation inside the opening of the connectingpiece, the length of the weld is reduced, but importantly the path ofthe welding head is greatly simplified. This is of particular benefit inthe case of friction stitch welding, where high reaction forces arerequired in the supporting structure.

It is noted at this point that GB-A-2040202 discloses a method andapparatus for welding a hollow member to a tubular member using a laserwelding head that is disposed into the hollow member. The workpiece isrotated to form an internal weld between the hollow member and thetubular member. This known method and apparatus are for use in formingtubular steel structures, presumably on land, and there is notsuggestion of their use in forming fluid connections generally, or or“hot tapping” in particular

The welding operation may in particular comprise a friction weldingoperation, such as friction stitch welding. The welding may be performedwithout use of a hyperbaric chamber, and without pre-heating thematerial of the first wall or connecting piece. The method may beperformed as part of a hot-tapping operation in a working installation,or during construction. The method may be performed onshore or offshore,and may be performed under water.

The first wall at the tap location may be a curved surface. The firstwall may for example be a pipe wall. The connecting piece in this casewill generally comprise a saddle-shaped member.

The connecting wall may provide a flange mounting at its end remote fromthe mounting surface, for connecting said conduit over the opening ofthe connecting piece. The opening in the connecting piece may be formedlarger than the aperture formed at the tap location, in accordance withthe dimensions of a welding head. In any case, however, the formation ofthe weld within the diameter of the connecting wall involves a weld ofsmaller dimensions and simpler shape than conventional methods, in whichthe weld extends around the outside of the saddle-shaped connectingpiece.

The welding step may be performed using a welding head carried on aframe adapted for connecting to the connecting piece, the welding headbeing driven within said frame to complete said welding operation atlocations within the opening and surrounding the tap location. In thecase of friction stitch welding, the welding head may be stepped tosuccessive locations, at each location fusing a plug of material to thematerial of the connecting piece and the first wall, the locationsultimately overlapping so as to form a continuous weld of said fusedmaterial.

The mounting surface of the connecting piece may extend at leastpartially over the tap location, the method including the step ofremoving material of the connecting piece. The removing step maycomprise cutting simultaneously through the material of the connectingpiece and the wall. At its simplest, the opening of the connecting piecemay be entirely closed until said material is removed.

In a preferred embodiment, the material is removed by cutting throughthe welded portions of the first wall and the connecting piece. Thisavoids leaving any gap between the two materials between the opening andthe weld, where fluid pressure and/or chemical attack would otherwisetend to open the weld. The material may alternatively be removed bycutting at a distance inside of the weld. This leaves a small gap, butnot on the scale of the prior art, where the weld is formed outside theconnecting wall altogether.

In accordance with a second aspect of the present invention there isprovided a method of hot-tapping a connecting piece to a pipeline orother surface, wherein the connecting piece has a central well, whichmethod includes locating the connecting piece, locating and fixing thewelding apparatus with respect to the connecting piece so that thewelding head of the apparatus can be operated within the well of theconnecting piece, boring a hole through a surface of the connectingpiece in the well and into the pipeline or other surface, locating aplug in the hole bored, applying a load with the welding head androtating the welding head and plug so that the frictional heat andpressure generated between the plug and sides of the bored hole causethe plug material to flow and form a weld, repeating the steps of boringa hole and forming a weld until a suitable welded joint is formed andcutting through the pipeline or other surface to form a flow passage.

The general method of welding used in this method is Friction StitchWelding. This is a solid phase operation, and problems with dissipationof heat and the need to continually supply this to the articles beingwelded are alleviated. This is due to the fact that as the heatgeneration between the plug and the sides of the bored hole can becontrolled to meet the required conditions.

In addition as a solid phase operation is being used there are no sparksor ignition sources being generated which means the method is suitablefor use in explosive environments.

In one embodiment of the invention the holes are bored and the weldsformed in an overlying pattern. The use of an overlying pattern enablesa continuous weld to be formed which surrounds the flow passage.

The connecting piece for use with the present invention may have a basein the central well which may be cut away at the same time as the wallof the pipeline to form the flow passage.

Further when the pipeline is cut to form the flow passage a part of thewelded joint may also be removed. By cutting away a part of the weldedjoint a smooth surface free from any crevices may be formed. A possiblesource of corrosion is thereby avoided.

In an alternative arrangement sealing means may be used to negate theexistence of crevices.

The present invention has been developed for use in situations wherehigh heat dissipation occurs, for example, where there is a large bodyof fluid adjacent the surface to which the hot-tap is being fitted.Typical examples of these circumstances are with a large vessel or tankwhere a valve is being fitted to during service, or sub-sea operations.

In both of these cases, an important factor to be considered is the sizeof the apparatus being used and the need to rotate the workpiece withrespect to said apparatus. Clearly with a hot-tap the apparatus has tobe rotated rather than the workpiece and when this is considered alongwith the need to transport the apparatus to the site size is important.

The invention further provides apparatus adapted for use in the methodsof the invention set forth above, and to apparatus and installationsformed by connecting two or more conduits or other vessels by themethods according to the invention, as set forth above.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, by reference to the accompanying drawings, in which:

FIG. 1 shows a schematic view of a pipeline having a connecting piecefitted thereto in accordance with the present invention;

FIG. 2 shows a schematic view of the welding head during the fitting ofthe connecting piece shown in FIG. 1;

FIG. 3 shows a schematic view of suitable welding pattern for forming ofa continuous weld;

FIGS. 4 a & 4 b show a first form of connecting piece fitted to apipeline;

FIGS. 5 a & 5 b show a second form of connecting piece fitted to apipeline; and

FIG. 6 shows a connecting piece fitted to a flat sided vessel.

Throughout the drawings, the legends “BC” and “AC” are used to show theoutline of the workpiece before cutting (BC) and after cutting (AC).

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 shows a pipeline 1 with a connecting piece 2 having an uppersection 2 a and a lower section 2 b located thereabouts. The innersurfaces of the upper and lower sections 2 a,2 b are curved so that whenfitted about a pipeline of the required diameter they engage the surfaceof the pipeline.

The lower section 2 b of the connecting piece comprises a longitudinallyextending semi-circular section with longitudinal flanges 2 c. Theflanges 2 c are each provided with a series of through-bores 2 d.

The upper section of the connecting piece 2 includes a longitudinallyextending semi-circular section with longitudinal flanges 2 e with aseries of through-bores 2 f provided therein. A main body section 2 g isprovided on the upper section 2 a and has a circumferentially extendingwall 2 h with a central well 2 k located within the wall 2 h. In theparticular example shown here the central well has a base 2 n.

Further fitting means 2 p are provided in the upper surface of the wall2 h for subsequent fitting of a pipe or other equipment as desired.

In use the upper and lower sections 2 a,2 b are fitted about the pipeline 1 so that the respective through-bores 2 d and 2 f are inalignment. The two sections of the connecting piece are then boltedtogether and drawn into contact with the surface of the pipeline.

The connecting piece 2 may then be friction stitch welded to thepipeline. To do this welding apparatus 3 is located on the wall 2 h ofthe connecting piece and bolted in place in fixing means on theconnecting piece. In this example the fixing piece comprises a simpleflange seat provided with threaded holes 2 p in the upper surface of thewall 2 h. The apparatus 3 may include a rotatable welding head 4 withdrive motor 5 which is mounted so that it may be positionally adjustedwith respect to the connecting piece. The positional adjustment may beboth vertically and axially about an axis extending vertically throughthe well 2 k of the connecting piece 2. The apparatus 3 in the FIG. 1 isshown schematically simply to show the location of the apparatus on theconnecting piece 2. In practice, the apparatus will comprise a frictionstitch welding head such as is described in the references cited in theintroduction, mounted on a frame, and driven by means (not shown) so asto step-rotate to each stitch position.

Referring also to FIGS. 2, 3 and 4, in operation, when the apparatus 3has been located on the connecting piece 2 a first hole is bored throughthe base of the central well 2 k of the connecting piece and into thewall of pipeline 1. The hole does not extend through the wall of thepipeline but extends into it, see FIG. 2 for greater detail. A plug 6 ofsuitable material is now located in the bore and the welding head of theapparatus lowered into position. The welding head of the apparatusengages the plug and applies a load while rotating the plug in the hole.The heat generated by the engagement of the plug with the sides of thehole is sufficient to plasticise melt the plug 6 so that the metal flowsunder pressure, forming a metallic bond with the parent material.

The above operation of boring a hole and forming a weld is repeateduntil the connecting piece is secured to the pipeline. To form acontinuous welded joint around circumference of the well 2 k the boresand welds are made so that they overlap, see FIG. 3 in a set sequence tomaximise efficiency. Typically, a spaced series of these “stitches” willbe made on a first pass, and then intermediate stitches are formed toprovide the overlap. Depending on the tooling arrangement, it may bepreferred to drill a number of bores in one phase of operation, and theninsert and drive the plugs in another phase.

When the weld has been formed, the base of the central well 2 k and thecorresponding section of the pipeline are cut free and removed.Throughout the drawings, the legends “BC” and “AC” are used to show theoutline of the workpiece before cutting (BC) and after cutting (AC). Inorder to avoid a lip in the surface formed by this cutting operation thecut may be made so that a part of the weld formed is also removed.Different types of cutting process may be envisaged, including thosegenerally known and used in prior hot tapping systems. The cutting canbe carried out for example with high precision mechanical trepanningcutter which is available on the market. It is preferable to ensure thatthe cut is made though the friction stitch weld in such a way that asmall part of the friction stitch weld is removed and no crevice remainson the cutting surface between the saddle fitting and the pipe surface.

It should be noted that the space required for operation of theapparatus 3 in the central well 2 k means that the well 2 k is of largerdiameter than is strictly required for the flow passage that will beformed in the connecting piece.

Once the weld has been formed and the flow passage accessed theapparatus 3 may be removed and a pipe or other desired equipmentattached to the connecting piece 2 by means of the flange seat 2 p. In ahot tapping situation, the open conduit must obviously be isolated fromthe surrounding environment. The solutions applied in known hot tappingsystems can be applied equally here.

Now referring to FIGS. 4 and 5 of the drawings there is shown two typesof connecting piece fitted to a pipeline with like components beinggiven like references. These two connecting pieces differ from oneanother in the shaping of the flange and are designed to meet differentoperational criteria.

While the invention has been described for fitting of a connecting pieceto a pipeline the method is equally suited to use with fixing a suitablefitting to other components. For example, for fitting of a connectingpiece or other fitting to another form of tubular section or a flatsection such as the wall of a vessel or tank. FIG. 6 of the drawingsshows the connecting piece 2 shown in FIG. 5 of the drawings adapted andfitted to a flat-sided vessel.

While the techniques described are particularly advantageous in thecontext of hot-tapping operations sub-sea, there is no reason why thesame should not be applied to hot tapping on land and structures abovewater, or to the construction of new installations, on- or off-site, aswell as the modification and repair of existing installations.

The specific embodiments and applications disclosed are in no waylimiting on the scope of protection sought, which will be defined by thelanguage of the appended claims.

1. A method of forming a tap through a metallic first wall at a desiredtap location, the method comprising: fitting against the metallic firstwall a metallic connecting piece which comprises (i) a metallic mountingsurface formed so as to fit directly against the metallic first wall and(ii) a metallic connecting wall surrounding the tap location providingan opening adapted for subsequent connection of a metallic conduit tocomplete said fluid connection, the material of said metallic mountingsurface further extending at least partially within said opening;bonding the material of the metallic connecting piece to that of themetallic first wall by means of a welding operation performed throughsaid opening, the resulting weld surrounding the tap location and beingsurrounded in turn by the metallic connecting wall; and subsequentlyremoving the material of the metallic first wall at the tap locationthereby to define an aperture and provide said conduit to complete saidfluid connection surrounded by the weld between the metallic connectingpiece and the wall.
 2. A method according to claim 1, wherein the methodis performed as part of a hot-tapping operation in a workinginstallation.
 3. A method according to claim 1, wherein the method isperformed off-line as part of construction.
 4. A method according toclaim 1, wherein the tap is formed under water.
 5. A method according toclaim 1, wherein the metallic first wall at the tap location is a curvedsurface.
 6. A method according to claim 1, wherein the metallic firstwall is a pipe wall, and the metallic connecting piece comprises asaddle-shaped mounting surface.
 7. A method according to claim 1,wherein the metallic connecting wall provides a flange mounting at itsend remote from the metallic mounting surface, for connecting saidmetallic conduit over the opening of the metallic connecting piece.
 8. Amethod according to claim 1, wherein the opening in the metallicconnecting piece is formed larger than the aperture formed at the taplocation, in accordance with the dimensions of a welding head used inthe welding operation.
 9. A method according to claim 1, wherein thewelding operation is performed using a welding head carried on a frameadapted for connection to the metallic connecting piece, the weldinghead being driven within said frame to complete said welding operationat locations within the opening and surrounding the tap location.
 10. Amethod according to claim 9, wherein the welding head is stepped tosuccessive locations, at each location fusing a plug of metallicmaterial to the metallic material of the metallic connecting piece andthe metallic first wall, the locations ultimately overlapping so as toform a continuous weld of said fused material.
 11. A method according toclaim 1, wherein the welding operation is a friction welding operation.12. A method according to claim 1, wherein the metallic mounting surfaceof the metallic connecting piece extends at least partially over the taplocation, the method including the step of removing material of themetallic connecting piece.
 13. A method according to claim 12, whereinthe step of removing material comprises cutting simultaneously throughthe metallic material of the connecting piece and the wall.
 14. A methodaccording to claim 13, wherein the material is removed by cuttingthrough the welded portions of the metallic first wall and the metallicconnecting piece.
 15. A method according to claim 1, wherein saidwelding operation comprises: boring a hole through the metallic mountingsurface of the metallic connecting piece within the opening and into themetallic first wall, locating a metallic plug in the hole bored,applying a load with a welding head and rotating the welding head andplug so that frictional heat and pressure generated between the plug andsides of the bored hole cause the metallic plug material to flow andform a weld, repeating the steps of boring a hole and forming a welduntil a continuous welded joint is formed, and cutting through themetallic first wall to form a flow passage surrounded by said weldedjoint.
 16. A method of forming a tap through a metallic first wall at adesired tap location, the method comprising: fitting against themetallic first wall a metallic connecting piece which comprises (i) ametallic mounting surface formed so as to fit directly against themetallic first wall, and (ii) a metallic connecting wall surrounding thetap location and providing an opening adapted for subsequent connectionof a metallic conduit to complete said fluid connection, the material ofsaid metallic mounting surface extending at least partially within saidopening; bonding the material of the metallic connecting piece to thatof the metallic first wall by means of a welding operation performedthrough said opening; said welding operation comprising boring a holethrough the metallic mounting surface of the metallic connecting piecewithin the opening and into the metallic first wall, locating a metallicplug in the hole thus bored, applying a load with a welding head androtating the welding head and plug so that frictional heat and pressuregenerated between the plug and the bored hole cause the metallic plugmaterial to flow and form a weld, and repeating the steps of boring ahole and forming a weld until a continuous welded joint is formed; andcutting through at least the metallic first wall at the tap location todefine an aperture to provide said fluid connection, the aperture beingsurrounded by said welded joint.
 17. The method of claim 16, in whichsaid metallic mounting surface extends across and forms a closed end tosaid metallic connecting wall, and in which said cutting step isperformed through the welded joint to remove portions of both saidmetallic first wall and said metallic mounting surface to form saidaperture.